1. Field of the Invention
The present invention relates to a lock-up control device for a torque converter with a lock-up clutch in an automatic transmission, and more particularly, to improvements in a learning control of the lock-up control system.
2. Description of the Prior Art
A torque converter used in an automatic transmission for a vehicle is provided with a lock-up clutch and is completely locked up during running at a high speed, as shown in FIG. 6. Moreover, the lock-up clutch is held in a slip lock-up mode, that is, in an engagement state in which the lock-up clutch is given a small degree of slip (target slip) in a predetermined intermediate speed range for the purpose of improving fuel economy and reducing vibration.
During a coasting lock-up control wherein the engine is in the idle running-condition with the accelerator pedal released in the lock-up region, an engagement capacity of the lock-up clutch must be made into a level corresponding to a lowered engine-output in order to maintain a predetermined slip degree. Otherwise, the lock-up clutch is rapidly engaged and torque fluctuations and shift shock occur. In order to avoid such problems, an engaging oil pressure of the lock-up clutch is lowered to a predetermined value.
In FIG. 6, a region except a complete lock-up region, a slip lock-up region and a coasting lock-up region is a converter region wherein a slip control is not performed.
An engaging oil pressure in the coasting lock-up region must be a oil pressure value which restricts torque fluctuations and shift shock and also does not degrade the response of increase in the engaging oil pressure when the accelerator pedal is redepressed. Since this oil pressure value is dispersed due to individual difference and aging of the torque converter, a learning control is performed with respect to a preset basic initial pressure.
In order to prevent the engagement shock of the lock-up clutch in the complete lock-up region and the slip lock-up region, the engaging oil pressure is raised again from a predetermined initial pressure which has been set according to a map or the like. However, since it is impossible to be freed from the individual difference and the aging as described above, a learning control is also performed in these two regions.
In the conventional automatic transmission, the above learning control is separately executed in each of the complete lock-up region, the slip lock-up region and the coasting lock-up region. For example, in order to obtain a learning correction amount suitable for correcting a basic initial pressure in the coasting lock-up region, therefore, a coasting lock-up control must be repeated for a long time period and requires a considerably long time. This disadvantage applies also to the complete lock-up region and the slip lock-up region.
The present invention has been made in view of the aforementioned conventional problem, and it is an object to provide a lock-up control device for a torque converter of an automatic transmission which is capable of realizing a proper learning control of an engaging oil pressure of a lock-up clutch of the torque converter in a short time period.
To accomplish this object, the present invention provides a lock-up control device for a torque converter of an automatic transmission equipped with a lock-up clutch, including learning control means for performing a learning control of an initial command oil pressure for a lock-up control for each of plurality of lock-up regions according to vehicle running condition, the learning control means setting the initial command oil pressure by adding a lock-up learning correction amount to a basic initial pressure set for each of the plurality of lock-up regions, and setting an initial command oil pressure of a lock-up control of one of the plurality of lock-up regions by using a lock-up learning correction amount calculated by a learning control in a lockup control of the other of the plurality of lock-up regions when the lock-up control of the other of the plurality of lock-up regions is performed before the lock-up control of the one of the plurality of lock-up regions.
In the one of the plurality of lock-up regions, an initial command oil pressure is determined by adding a lock-up learning correction amount calculated in the learning control performed in the other lock-up regions to a basic initial pressure, and hence the use of the learning result obtained in the other lock-up regions allows a proper basic initial pressure to be quickly achieved.
The one of the plurality of lock-up regions may be a coasting lock-up region with the other of the plurality of lock-up regions being a slip lock-up region or a complete lock-up region, or the one of the plurality of lock-up regions may be a slip lock-up region or a complete lock-up region with the other of the plurality of lock-up regions being a coasting lock-up region.
Since a lock-up learning correction amount can be commonly used among three kinds of lock-up regions, a lock-up as set is early realized in each lock-up region.
The above and further objects and features of the invention will be more fully apparent from the following description when the same is considered with reference to the accompanying drawings.